Spin injection into semiconductors has seen large progress over the last years. With the theoretical understanding of the basic problems of diffusive injection of spin polarized electrons into semiconductors, various concepts using highly spin polarized materials and different kinds of barriers have been realized. The presentation will give an overview on the theory of spin injection and major experimental work done in the last years. In addition novel devices like voltage dependent spin filters will be presented. Moreover, recent experiments will be shown in which domain walls in ferromagnetic semiconductors were trapped in nanoconstrictions, leading to magnetoresistance effects of up to 2000 %.